1. Field of Invention
The invention relates to the field of photography, and more specifically to cameras, methods of advancing film, and film metering devices, particularly for half-frame exposures.
2. Description of the Prior Art
A typical mechanism for metering film is exemplified by a commercially available single use camera. The film is advanced by a thumb wheel to move sequentially, one frame after another, across an exposure plane between supply and take-up chambers. The metering mechanism includes a sprocket wheel and coaxial cam that are driven by perforations along an edge of the film to rotate the cam one revolution for each exposure frame. The cam controls a metering lever that pivots into a notch in the cam when the film is properly positioned for the next exposure. An opposed arm on the metering lever then moves against teeth on the edge of the thumb wheel, preventing further movement of the film until the mechanism is released during the next exposure sequence. An exposure is initiated by releasing a latch that constrains a high energy striker. The striker drives a shutter blade open, pivots the metering lever from the cam notch, and releases the thumb wheel and film for advancement of the next frame. A single use camera of this type is described, for example, in U.S. Pat. No. 5,235,366, issued Aug. 10, 1993.
It also is known to provide camera mechanisms with metering devices suitable for half-frame exposures. Shyu U.S. Pat. No. 4,716,427, issued Dec. 29, 1987, is one example having alternative settings for full and half-frames. The settings adjust Opaque plates in the viewfinder and exposure box. The film metering mechanism uses a wheel with two depending pins, one longer than the other, that rotate with the wheel when the film is advanced. When the camera is set for a full frame exposure, the long pin controls a complete revolution of the wheel, which meters a full film frame into the exposure position. When set for half-frame exposures, both pins are used, limiting rotation of the wheel to half revolutions between exposures, and reducing film movement between exposures to to an amount suitable for half-frames.
Still other cameras expose multiple images in the same area normally covered by a full frame. Murphy U.S. Pat. No. 3,815,970, issued Jun. 11, 1974, is an example disclosing two optical systems that focus images on the film in stereo pairs. The paired images are aligned in abutting relationship along their adjacent edges.